This invention pertains to the field of smoking materials. More particularly, the present invention concerns a method fo upgrading tobacco by-product material, particularly tobacco stems, such that it will not possess its inherent "woody taste" and will be mild and possess low impact such that it can be incorporated into a smoking material.
As a result of the stripping of leaf tobacco in preparation for its use for cigar wrappers or fillers, cigarettes and smoking tobacco, tobacco by-products, such as, stems, stalks and leaf scraps are collected. These by-products have not been usable for direct incorporation in smoking product, although some have been used for making snuff and for mixture with chewing tobacco. Tobacco dust and the like have also been recovered from shipping and handling of tobacco. Although attempts have been made in the past to economically utilize these tobacco by-products by forming "reconstituted" tobacco therefrom (see, for example, U.S. Pat. Nos. 3,409,026 and 3,386,449), such reconstituted tobacco has frequently been found to be undesirable due to the harshness, poor aromatic qualities and off-taste of the smoke produced by this material even when it is combined with natural leaf tobacco and used in very small quantities. This is particularly true where attempts have been made to utilize Burley tobacco by-products.
Prior art techniques have utilized thermal degradation or "pyrolysis" of a carbohydrate or cellulosic material in an inert atmosphere for subsequent incorporation with tobacco leaf material. The pyrolysis carried out is such that it subjects the cellulosic or carbohydrate material to extreme thermal degradation such that a weight loss of generally about 60% or more is sustained by the treated material. The pyrolyzed material assumes a grayish-black color as a result of this treatment. Such techniques are disclosed, for example, in U.S. Pat. Nos. 3,861,401, 3,861,402 and 4,019,521.
The above techniques suffer from many disadvantages. In particular, they generally all require the addition of materials which are foreign to tobacco. These foreign materials may detract from and adversely affect the acceptability of the smoking product which contains such additives.
Moreover, the extreme thermal degradation which is carried out in these techniques is undesirable inasmuch as the material suffers structural breakdown, becomes brittle and unable to reabsorb moisture and retain the necessary flexibility. By exposing the material to controlled heat treatment which results in a weight loss of approximately 30%, the material will retain flexibility and moisture content comparable to the other portions of tobacco filler to which it is intended to be blended.